Bearings



United States Patent 3,370,006 BEARINGS Charles Campbell, Thames Ditton,England, assignor to Morganite Research and Development Limited, London,England, a corporation of England No Drawing. Filed Nov. 2, 1964, Ser.No. 408,366 Claims priority, application Great Britain, Nov. 6, 1963,43,832/ 63 6 Claims. (Cl. 25212) This invention relates to ananti-friction composition, anti-friction elements made therefrom, and tobearings and bearing assemblies including such elements.

Applicants have developed the use of nickel oxide and/ or cobalt oxidein bearing surfaces in order to obtain excellent lubrication and wearresistance at high temperatures. It is found that these oxides form apatina on the bearing surface and it is believed that this patinaprovides the anti-friction properties.

It has 110W been found however that, for some reason which is not clear,the nickel or cobalt oxide are prone to an undue amount of wear belowabout600? C. vThis is a substantial disadvantage since, although thenickel or cobalt oxides are designed for use with high temperatureengines and the like, such engines must pass through the lowertemperature ranges during starting up; it is then that the nickel oxideor cobalt oxide, and hence the bearing, is liable to be subjected toexcessive wear.

According to the present invention there is provided an anti-frictioncomposition containing nickel oxide and/ or cobalt oxide together with aless wear-resistant, high melting (i.e. above 700 C.) solid lubricantwhich is nonreducing at high temperatures. The requirement that thesolid lubricant must be non-reducing at high temperatures is set by theneed to ensure that there is no extensive reduction of the nickel oxideor cobalt oxide during use.

The melting point of the solid lubricant must be above 700 C. and mayhave to be higher depending on'the use to which theanti-frictioncomposition is put. It will be clear that the melting pointmust always be higher than any temperature that the composition mayreach during use.

Examples of solid lubricants that have been found effective includeGroup IIa fluorides, phosphates and borates, 6.g., Mg P O MgF Ca P OCaB40'1 and BaFz. Also found to be effective is lead monoxide. Aparticularly preferred solid lubricant is calcium fluoride which isfound to operate as a lubricant at temperatures up to 900 C., and it isparticularly efficient over the range 200-600 C. The solid lubricant ispreferably used in amounts of at least 5% by weight of the anti-frictioncomposition preferably 8-15% by weight of the composition. Suitably upto 25% by weight of the composition is present.

As stated above, the prime advantage of these solid lubricant additiveslies in the provision of wear-resistant properties at temperatures below600 C. They neverthe-v less also help in providing lubricatingproperties at higher temperatures.

Provided the anti-frictionelement is to be used in an oxidizingatmosphere, part of the cobalt or nickel oxides may be replaced bycobalt or nickel metal, which metal is then gradually oxidized in situ.There must, however, be sufiicient of these oxides present initially atthe hearing surface to ensure that the element provides lubricationimmediately on attaining the high temperatures, e.g.,

at least 30% of the bearing surface being the oxide. The oxidation insitu of the metal must be sufiicient to replace continuously the oxidepatina as it is worn away.

It has'been'found desirable for some purposes to include in theantifriction composition oxides which form eutectic. mixtures withnickel and/or cobalt oxide. Examples of these are aluminium, magnesium,zinc and stannic oxides and titanium dioxide, and mixtures of these. Theprime advantage in including these oxides is that they form a eutecticwith all on some of the nickel oxide and/ or cobalt oxide, depending onthe quantity added, and thus reduce the temperatures required forsintering or other coating processes.

To prepare a mix of the various components of the anti-frictioncomposition, both ball milling and dry blending have been foundsuitable. The anti-friction composition may be formed into antifrictionelements providing bearing surfaces. Thus the composition may be used toprovide the bearing surfaces in a bearing assembly incorporating aplurality of elements bearing against one another.

Preparation of the anti-friction elements may be by any suitable method,the most preferred being by sintering or flame-spraying the aforesaidcomposition on to a suitable substrate. Other methods available includebonding of the composition on to the substrate in an enamel, asdisclosed in our pending British patent application No. 9,745/63. Thebearing surfaces may be applied directly'to the substrates, or anintermediate undercoat may be used as desired. 7

The substrates used for the bearings may be chosen to provide theoptimum mechanical and other properties. 'So far as possible it shouldbe arranged that the coefiicient of expansion of the substrate and thatof the bearin surface are substantially the same. It has been found-thatbearings using the anti-friction composition of the present inventionwork almost equally effectively over the entire temperature range 201000 C.

It is foreseen that bearing surfaces prepared from the anti-frictioncomposition of the present invention will have many applications, amongwhich may be mentioned the Cercor (honeycomb ceramic) heat exchanger(Cercor is a trademark) and rotary piston internal combustion engines ofthe Wankel type.

The invention illustrated in the following examples.

Example 1 A mix was prepared containing:

Green nickel oxide 900 Calcium fluoride The above quantities wereweighed out and milled dry for 6 hours in a 10" diameter rubber linedball mill at 60 rpm. with 1 kg. of l alumina cretoids.

The milled material was passed through a 100 mesh B.S. sieve andtransferred to a Z bladed mixer. About 200 gm. ofan extrusion binder wasthen mixed in to produce an extrudable composition. The extrusion binderused-was that sold underthe trademark Cellofas. This, binds theparticulate material together during shaping and handling, butdecomposes during firing so that only the original components remain. I

Rods were extruded from the composition prepared as above, and sinteredby firing to 1440 C. in an air atmosphere.

Coatings of the material were then applied to a stainless steelsubstrate with an undercoat of a nickel-chromium alloy by flame-sprayingby the Rokide (trademark) process.

Bearings obtained by this method were used in a Cercor heat exchanger.At 600 C., 100 ft./min., lbs. load, wear rates of 0.00003 per hour wererecorded.

Example 2 A mix was prepared containing:

. Gms. Green nickel oxide (200 RS. mesh) 750 Calcium fiouride (300 RS.mesh) 250 The powders were intimately mixed by dry blending, and thenflame-sprayed on to a substrate prepared in the normal manner.

Instead of flamespraying the powders directly after mixing, they may bepressed into blocks and sintered at 1250 C. Following the sintering theyare then crushed and sieved through 200 B5. mesh on to 300 B5. mesh, andsubsequently frame-syrayed as above.

Examp'le3 A further mix was prepared containing:

. Gms. Green nickel oxide (200 RS. mesh) 950 Lead oxide (PbO) (300 ES.mesh) 50 The powders were mixed by dry blending and flamesprayed on to asubstrate as in Example 2. In this case sintering was carried out at1500 C.

Bearing surfaces prepared from this mix had good running properties overa wide range of temperatures. They were also found to have a smallercoeflicient of expansion than the mix of Example 2.

Example 4 The wear rate of bearings made according to this invention wasmeasured by forming a /8" diameter pad of bearing material, and holdingit in sliding contact with the underneath stellite-coated surface of acounterface rotating about a vertical axis. The wearrate was determinedby observing the weight loss per hour of the bearing material, andconverting this figure into the mean thickness of the material havingthe same weight as that lost. The tests were carried out with apredetermined pressure between the pad of bearing material and thecounterface, i.e., a predetermined bearing load, and the apparatus wascontained in a heated chamber. The re- 4 Examp'le6 Percent NiO 90 Mg P OExample 7 Percent CoO 85 PhD 15 Example8 Percent NiO 90 (2313 07Example9 Percent C00 85 CaF What is claimed is:

1. A wear-resistant element comprising a composition flame-sprayed ontoa substrate, said composition consisting essentially of at least oneoxide selected from the group consisting of nickel oxide and cobaltoxide, together with a material selected from the group consisting oflead monoxide, and fluorides, phosphates and borates of Group Ila metalsin an amount of from 5 to 25% by weight of the composition.

2. A wear-resistant element comprising a composition flame sprayed ontoa substrate, said composition consisting essentially of at least oneoxide selected from the group consisting of nickel oxide and cobaltoxide, together with a material selected from the group consisting ofmagnesium pyrophosphate, calcium pyrophosphate, calcium pyroborate,magnesium fluoride and barium fluoride in an amount of from 5 to 25% byweight of the composition.

3. A wear-resistant element comprising a composition flame-sprayed ontoa substrate, said composition consisting essentially of at least oneoxide selected from the group consisting of nickel oxide and cobaltoxide, together with calcium fluoride in an amount of from 5 to 25% byweight of the composition.

4. A wear-resistant element comprising a composition flame-sprayed ontoa substrate, said composition consisting essentially of (1) at least onefirst oxide selected from sults of the experiments are tabulated below:the group consisting of nickel oxide and cobalt oxide,

TABLE 1 Test Temp, Bearing Surface Counter- Wear- Material N 0. C. load,speed, lace rate, 10-

p.s.i. It. p.111. inJhr.

NiO 400 25 A 0.3 Wt. NiO and 1 400 60 25 A 0. 49 35% Wt. CaFg. 2 400 6025 B O. 45 90% wt. NiO and 1 400 60 25 A 0. 09 10% Wt. CaFz. 2 400 60 25B 0. 06

Examples 5-9 ExampleS Percent NiO 50 C00 4O CaF 10 (2) a materialselected from the group consisting of lead monoxide and fluorides,phosphates and borates of Group Ila metals in an amount of from 5 to 25%by weight of the composition, and (3 at least one second oxide selectedfrom the group consisting of aluminum oxide, magnesium oxide, zincoxide, stannic oxide and titanium dioxide, the first and second oxidesbeing present in substantially-eutectic proportions.

5. A wear-resistant element comprising a composition flame-sprayed ontoa substrate, said composition consisting essentially of (1) at least oneoxide selected from the group consisting of nickel oxide and cobaltoxide in an amount of at least 30% by weight of the composition,

(2) at least one metal selected from the group consisting of nickel andcobalt in an amount ranging from a trace up to 65% by weight of thecomposition, and (3) a material selected from the group consisting oflead monoxide, and fluorides, phosphates and borates of Group IIa metalsin an amount of from 5 to 25% by weight of the composition.

6. The wear-resistant element of claim 4 wherein said material iscalcium fluoride.

6 References Cited UNITED STATES PATENTS 3,122,505 2/1964 Rulon-Milleret a1. 252-12 3,125,519 3/1964 Graue et a1 252-12 3,297,571 1/1967 Bonis252-12 DANIEL E. WYMAN, Primary Examiner.

I. VAUGHN, Assistant Examiner.

5. A WEAR-REAISTANT ELEMENT COMPRISING A COMPOSITION FLAME-SPRAYED ONTOA SUBSTRATE, SAID COMPOSITION CONSISTING ESSENTIALY OF (1) AT LEAST ONEOXIDE SELECTED FROM THE GROUP CONSISTING OF NICHEL OXIDE AND COBALTOXIDE IN AN AMOUNT OF AT LEAST 30% BY WEIGHT OF THE COMPOSITION, (2) ATLEAST ONE METAL SELECTED FROM THE GROUP CONSISTING OF NICKEL AND COBALTIN A AMOUNT RANGING FROM A TRACE UP TO 65% BY WEIGHT OF THE COMPOSITION,AND (3) A MATERIAL SELECTED FROM THE GROUP SONSISTING OF LEAD MONOXIDE,AND FLUORIDES, PHOSPHATES AND BORATES OF GROUP IIA METALS IN AN AMOUNTOF FROM 5 TO 25% BY WEGHT OF THE COMPOSITION.